While an i7 is a superior processor. The gain in gaming performance in most games is minimal usually less than. It's only a few games where an i7 will really make a difference. That is only if you have a very high end GPU playing at a lower resolution. So that the CPU becomes a limiting factor in FPS.
Now that money you would spend on a Core i7, Motherboard, RAM and don't forget a new Windows license. Would be better spent on buying a GeForce GTX 1080 8GB. Which will have a far greater impact on gaming than going from an FX-8350 to an i7. If you don't already have a GTX 1080 that is. Now if you already have a GTX 1080 8GB. Then by all means an Intel Core i7 6700K would make a great companion. Don't put the cart before the horse.